Threaded fastener having a thread crest greater than its thread root and &#34;V&#34; angles on the crest and root

ABSTRACT

An interlocking thread with a tooth-cross-section that is wider at its crest than at its root and with “V” angles located both along the crest and the root which tightens into a tapped hole that has a similar thread cross-section.

FIELD OF THE INVENTION

The following invention relates generally to fasteners. Moreparticularly, this invention pertains to the field of fasteners havingan exterior thread located peripherally about the shaft of the fastener,in which the thread spirals along a portion of the shaft. Mostspecifically, the thread, when taken in cross-section, has a contourwhich increases in a dimension as it extends radially away from a rootto a crest of the thread. “V” angles are located along the crest androot.

BACKGROUND OF THE INVENTION

Threaded fasteners are extremely old devices which exhibit superiorholding properties over non-threaded fasteners primarily due to a highercoefficient of friction. This coefficient of friction is manifestedalong the inter-face of the threads to its connecting environment.Fasteners where the threaded portion exhibits a dovetail when viewed incross-section define one specie of threaded fastener.

Pat. No. Issue Date Inventor 6,572,315 Jun. 3, 2003 Reed

Applicant herein, Reed, teaches the use of a fastener which benefitsfrom dovetail geometry. While the structure provides excellent benefits,the instant disclosure takes that technology to the next level.

BRIEF SUMMARY OF THE INVENTION

This invention is a new type of thread combination that has the sameability to tighten while creating a radial clamping action as in theearlier patent.

The thread can also be applied to metal stitching pins used to repaircracked and damaged castings. The present invention makes it much easierto repair thin wall castings that currently are very difficult torepair.

This new thread design creates an instant interlocking thread union,vertical loading capability, no counter bore or shoulder required andvery good resistance to vertical shear and bending loads. The uniqueinterlocking “double hook” contact surfaces, separated by “V” angles,prevent spreading or drawing forces from occurring when the fastener istightened. Where vertical loading is required or when no radialspreading or drawing force is desired, such as a set screw, superiorperformance is exhibited.

The structure according to the present invention is appreciably strongerin retarding axial translation both of the fastener and the materialwithin which the fastener is located. Further, the fastener hasappreciably greater strength in resisting bending moments, resistingtorsional flexure.

Specifically, first there is an interlocking grip of the double opposinghook threads that prevent outward movement of the sidewalls of thefemale object.

Second there is a continued gripping of the sidewalls in the event ofvertical upward or downward loading.

Third there is resistance to vertical shear loads in situations where itis used to attach sidewalls together.

Fourth there is resistance to bending moments where bending of joinedsidewalls is probable.

Fifth there is increased sealing ability of the threaded joint due toits complexity where a gas and/or liquid tight seal is required.

Sixth there is the ability to form this thread by conventional threadrolling processes which make it possible to manufacture cost effectivelyenough to compete with standard bolts and screws.

OBJECTS OF THE INVENTION

Viewed from a first vantage point, it is an object of the presentinvention to provide a fastener, comprising, in combination:

-   -   a shaft having a first end including means to rotate said shaft,    -   said shaft having a thread projecting from an outer periphery of        said shaft and spiraling along its length,    -   said thread defined by an upper flank, a lower flank, a root        adjacent said shaft and a crest remote from said shaft,    -   said thread defining a dovetail when viewed in section such that        said upper and lower flank of one dove tail section diverge        outwardly from each other away from said root,    -   said fastener having an indentation on said crest.

Viewed from a second vantage point, it is an object of the presentinvention to provide a fastener, comprising, in combination:

-   -   a shaft having a first end including means to rotate said shaft,    -   said shaft having a thread projecting from an outer periphery of        said shaft and spiraling along its length,    -   said thread defined by an upper flank, a lower flank, a root        adjacent said shaft and a crest remote from said shaft,    -   said thread defining a dovetail when viewed in section such that        said upper and lower flank of one dove tail section diverge        outwardly from each other away from said root,    -   said fastener having a projection on a gap between adjacent said        roots.

These and other objects will be made manifest when considering thefollowing detailed specification when taken in conjunction with theappended drawing figures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view of the threaded fastener having a portion cut awayto show the thread profile.

FIG. 1A amplifies the cut away.

FIG. 2 reflects the fastener as it engages a complementary bore andforce dissipation vectors.

FIG. 3 reflects a tapered shaft and shear load reactions.

FIG. 4 is a side view of the tap.

FIG. 4A is a top view of the tap.

FIG. 4B is a bottom view of the tap.

DESCRIPTION OF PREFERRED EMBODIMENTS

Considering the drawings, wherein like reference numerals denote likeparts throughout the various drawing figures, reference numeral 10 isdirected to the threaded fastener according to the present invention

In general, the fastener 10 includes a shaft 2 preferably ofsubstantially cylindrical configuration or with a taper. FIG. 3 shows atapered fastener. If the female bore (which receives the fastener FIG.2) is dimensioned greater than the smallest taper diameter of thefastener 10 but smaller than the greatest taper diameter of the fastener10, an interference fit results, similar to having varying thread pitch(i.e. increasing from “bottom” to “top”).

The fastener 10 has a first end 4 adjacent a “top” thereof and a secondend 6 defining a “bottom”. Note that the use of terms such as “top”,“bottom”, “horizontal”, etc. are made relative to the drawings appendedherewith but are not intended to be directionally limiting. First end 4may include means to rotate the shaft, such as a hex head or recess H.

The shaft 2 includes an integrally formed thread 12 spirally deployedthereabout. In one embodiment, any cross-section of the thread wouldappear as a dovetail having an upper pressure angle or flank 16 on a topside thereof and a lower pressure angle or flank 17 on a lower sidethereof. The outer surface extending between the upper flank and lowerflank defines a crest. The dovetail is supported on the shaft 2 by theroot. Areas on the shaft 2 between adjacent dovetails define root gaps18.

Threaded member 10 of FIG. 1 has a longitudinal axis 11 which passesthrough the center of the member. An external thread portion 12 ishelically wound around the circumference of the member 10. The externalthread portion 12 is defined between a minor diameter 13 (at root gap18) and crest diameter 14.

Interlocking pressure angles (upper) 16 and (lower) 17 are locatedbetween the crest diameter 14 and the minor diameter 13. Male and female“V” angles 19 and 20 are found with the male “V” angle 19 at the rootgap 18 and female “V” angle 20 at the exterior crest surface of thepressure angles 16 and 17.

In section, each upper pressure angle 16 is parallel to its others.Similarly, each lower pressure angle 17 is parallel to its others. Anincluded angle α between an upper and lower pressure angle may rangebetween 14 and 34 degrees and is preferably 24 degrees.

The root gaps 18 are interrupted by projections which define male “V”angles 19. The “V” shaped pressure angles 19 are formed (in section) bytwo angle surfaces 19 a and 19 b which converge as they extend fromshaft 2. Preferably, the projections 19 a, b define a “V” angle havingan acute apex remote from the shaft 2. The subtended acute angle βranges between 65-85 degrees, and preferably is 75 degrees.

The fastener's crest includes a female “V” angle 20 formed (in section)by two angle surfaces 20 a and 20 b which converge as they extendtowards the shaft 2. These surfaces 20 a, b define an indentation in thecrest thread and form a “V” angle having an acute angle γ where thesurfaces converge. Preferably the angle “γ” is 60 degrees and can rangefrom 50 to 70 degrees.

It is preferred that the gap 18 and the crest periphery 22 retain(respectively) shaft material and thread material. That is, the “V”angles should not extend all the way to the extremities of pressureangles 16, 17. This adds strength to resist shear, torsion, bending, andvertical loading parallel to the long axis 11.

FIG. 2 shows a female threaded section 30 with a similar internalthreaded profile engaged with a male threaded section 10 to create aninterlocking joint. The significance of this instant invention isnotably found in the benefits of function when the thread profile isengaged into a matching profile. Several unique and importantinteractions occur as the helical rotation causes abutted clamping forcebetween two objects.

First there is the interlocking grip of the double opposing hook threadsthat prevent outward movement of the sidewalls of the female object.

Second there is the continued gripping of the sidewalls in the event ofvertical upward or downward loading. FIG. 2 shows a vertical down load Abeing opposed by the fastener's reaction forces B, C, D, E, F and G. Acompressive load, by adding up load M, produce the same reactive forceson the thread, as would a tensile load (i.e. with load A and M inopposite outward directions. Specifically, compressive load M contactwith surfaces B, G, and D, while load A is opposed by C, E and F.

Third there is the resistance to vertical shear loads in situationswhere it can be used to attach sidewalls together. FIG. 3 shows shearloads J and H opposed by forces B, C, D, E, F and G.

Fourth there is the resistance to bending moments where bending ofjoined sidewalls is probable. FIG. 2 shows a bending moment BM opposedby surfaces/reaction forces B, C, D, E, F and G.

Fifth there is the increased sealing ability of the threaded joint dueto its complexity (surface to surface contact, e.g. FIG. 2) where gasand/or liquid tight seal is required.

Sixth there is an ability to form this thread by conventional threadfabricating processes such as cold rolling. Here, the pressure flanks16, 17 are flared outwardly during formation of the female “V.” In otherwords, the flanks 16, 17 are first formed parallel to each other andthen swaged outwardly which make it possible to manufacture costeffectively enough to compete with standard bolts and screws.

FIGS. 4, 4A and 4B show the tap 40 which forms the bore 30. In essence adriving head 42 rotates the tap 40 so that the flutes remove material.The contour of the flute mirrors the fastener (detailed in FIG. 1A) andbears similar reference numerals (incremented by 100). Thus 116 and 117are cutting elements that form the upper and lower pressure angle flanks16, 17 respectively. Male “V” angle 19 and female “V” angle 20 areformed by cutting elements 119 and 120 respectively.

Cutting elements 119 and 120 are especially important in that theyremove material providing clearance in advance of and in concert withcutting elements 116 and 117, making it possible to form the dovetailthreads in a single tapping process. This avoids sequential tappingwhich therefore avoids potential problems of misalignment when tappingin multiple steps—not to mention added time required.

I claim:
 1. A fastener, comprising, in combination: a shaft having afirst end including means to rotate said shaft, said shaft having athread projecting from an outer periphery of said shaft and spiralingalong its length, said thread defined by an upper flank, a lower flank,a root adjacent said shaft and crest remote from said shaft, said threaddefining a dovetail when viewed in section such that said upper andlower flank of one dove tail section diverge outwardly from each otheraway from said root, said fastener having an indentation on said crest.2. The fastener of claim 1 wherein said indentation is located inboardfrom crest extremities.
 3. The fastener of claim 2 wherein saidindentation is defined by two surfaces converging towards its root. 4.The fastener of claim 3 wherein said two surfaces form a “V” angle,having an acute angle where said surfaces converge.
 5. A fastener,comprising, in combination: a shaft having a first end including meansto rotate said shaft, said shaft having a thread project threadprojecting from an outer periphery of said shaft and spiraling along itslength, said thread defined by an upper flank, a lower flank, a rootadjacent said shaft and crest remote from said shaft, said threaddefining a dovetail when viewed in section such that said upper andlower flank of one dove tail section diverge outwardly from each otheraway from said root, said fastener having a projection on a gap betweenadjacent said roots.
 6. The fastener of claim 5 wherein said projectionis located inboard a base of adjacent said roots.
 7. The fastener ofclaim 6 wherein said projection is defined by two surfaces convergingaway from said shaft.
 8. The fastener of claim 7 wherein said twosurfaces form a “V” angle, having an acute angle where said surfacesconverge.
 9. The fastener of claim 4 including a complementally formedtap to provide a bore for the fastener.
 10. The fastener of claim 8including a complementally formed tap to provide a bore for thefastener.